Here's my problem and forgive me if the lingo is wrong. Our home is over 100 years old, it doesn't have typical framing. The corners of the house have what appear to be something like 6x6 beams running the entire height of the house. I have one that has rotted at the bottom (no foundation) which was sitting on what I call the plate' which was sitting on some rocks which were cemented in to form a footing. My question is... how can i lift this corner while I pour new footers and replace the damaged section as well. My main question is how can I repair this upright?

I have one that has rotted at the bottom
how can i lift this corner while I pour new footers and replace the damaged section as well. My main question is how can I repair this upright?

How many vertical inches of the post bottom are rotted?
By how much do you need to raise the post?
Calculating the vertical compressive force on that post may not be too difficult. A 20' high wood post of this cross section by itself may weigh [1/2][1/2][20][35] = ~180#.
How many sq. ft on each floor?
How many floors?

Can you put horizontal metal rods through the unrotted sections of the post and then pour enough concrete on top of the existing material so that the rods are now embedded in the new concrete and they now support the post?

Alternatively, bolt angle irons to the post corners and then do the concrete thing as above.